Box heater including a perforated flame holder

ABSTRACT

An enclosed heater includes a plurality of tubes (or a continuous serpentine tube) and a perforated flame holder within an interior volume. The plurality of tubes carries a working fluid. The perforated flame holder supports a combustion reaction of fuel and oxidant within the perforated flame holder and radiates heat to the tubes to heat the working fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit from U.S. ProvisionalPatent Application No. 62/117,429, entitled “BOX HEATER INCLUDING APERFORATED FLAME HOLDER,” filed Feb. 17, 2015 (docket number2651-272-02); which, to the extent not inconsistent with the descriptionherein, is incorporated by reference.

SUMMARY

According to an embodiment, an enclosed heater includes a plurality ofwalls forming an enclosure. The enclosure defines an interior volume. Aplurality of tubes are (or a continuous serpentine tube is) positionedalong the walls within the interior volume. A working fluid flowsthrough the tubes. A perforated flame holder is also positioned withinthe interior volume. A fuel and oxidant source outputs fuel and oxidantonto the perforated flame holder. The perforated flame holder supports acombustion reaction of the fuel and oxidant within the perforated flameholder. The perforated flame holder absorbs heat from the combustionreaction and radiates heat to the tubes, thereby transferring heat fromthe combustion reaction to the working fluid within the tubes. Accordingto an embodiment, the enclosed heater can include a box heater, a cabinheater, or a vertical cylinder heater.

According to an embodiment, a method includes outputting fuel andoxidant onto a first perforated flame holder positioned within aninterior of an enclosed heater. The enclosed heater includes one or morewalls defining the interior. The method further includes supporting amajority of a combustion reaction of the fuel and oxidant within thefirst perforated flame holder, passing one or more working fluidsthrough a plurality of tubes lining one or more walls within theinterior, and transferring heat from the first perforated flame holderto the one or more working fluids.

According to an embodiment, a box heater including an enclosure and atube including a first segment positioned external to the enclosure, asecond segment positioned within the enclosure, and a third segmentpositioned external to the enclosure, the second segment connecting thefirst segment to the third segment. The tube is configured to pass aworking fluid from the first segment, through the second segment, to thethird segment. The box heater further includes a fuel and oxidant sourcepositioned within the enclosure and configured to output fuel andoxidant, and a perforated flame holder positioned to receive the fueland oxidant, to sustain a combustion reaction of the fuel and oxidantwithin the perforated flame holder, and to transfer heat from thecombustion reaction to the working fluid as the working fluid passesthrough the second segment positioned within the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an enclosed heater, according to one embodiment.

FIG. 2 is a simplified perspective view of a burner system including aperforated flame holder, according to an embodiment.

FIG. 3 is a side sectional diagram of a portion of the perforated flameholder of FIGS. 1 and 2, according to an embodiment.

FIG. 4 is a flow chart showing a method for operating a burner systemincluding the perforated flame holder of FIGS. 1, 2 and 3, according toan embodiment.

FIG. 5A is perspective view of a cabin heater, according to anembodiment.

FIG. 5B is a top view of the cabin heater of FIG. 5A, according to anembodiment.

FIG. 5C is a cross-section of the cabin heater of FIG. 5A, according toan embodiment.

FIG. 5D is a side view of an interior of the cabin heater of FIG. 5A,according to an embodiment.

FIG. 6 is a side view of an interior of a box heater including multipleperforated flame holders, according to an embodiment.

FIG. 7 is a side view of the interior of a box heater including multipleperforated flame holders, according to an embodiment.

FIG. 8 is a flow diagram of a process for operating an enclosed heaterincluding a perforated flame holder, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. Other embodiments may be used and/or other changesmay be made without departing from the spirit or scope of thedisclosure.

FIG. 1 is a block diagram of an enclosed heater burner system 100,according to one embodiment. The enclosed heater burner system 100includes a wall 110 enclosing an enclosed heater interior volume 112. Aperforated flame holder 102 is positioned within the enclosed heaterinterior 112. A fuel and oxidant source 104 is positioned to output fueland oxidant onto the perforated flame holder 102. Tubes 106 carry aworking fluid 108.

According to an embodiment, the fuel and oxidant source 104 outputs fueland oxidant onto the perforated flame holder 102. The perforated flameholder 102 supports a combustion reaction of the fuel and oxidant withinthe perforated flame holder 102. The perforated flame holder 102 absorbsheat from the combustion reaction within the perforated flame holder102. The perforated flame holder 102 radiates heat to the tubes 106lining the wall 110 of the enclosed heater burner system 100. Theworking fluid 108 is passed through the tubes 106. Heat is transferredfrom the tubes 106 to the working fluid 108. In this way, heat istransferred from the perforated flame holder 102 to the working fluid108. The working fluid 108 is passed via the tubes 106 to the exteriorof the enclosed heater burner system 100 and is used to provide heat toan external apparatus. According to an embodiment, the working fluid 108transfers heat to crude oil flowing through a crude oil pipeline. Inanother embodiment the crude oil itself can be used as the working fluid108. Even and predictable radiative heating provided by the perforatedflame holder 102 can substantially prevent coking and other infirmitiesof conventional flame heaters. This may be used to simplify the designto allow even an inconsistent working fluid, such as crude oil with anasphaltene component, to avoid coking in the tubes 106. Moreover,whether or not a conventional 2-step working fluid-to-heat sink transferis used, the perforated flame holder 102 provides very low output ofoxides of nitrogen (NOx) and carbon monoxide (CO).

According to an embodiment, the enclosed heater defines an interiorvolume that is between 5 and 30 feet in height, length, and width.

According to an embodiment, the enclosed heater burner system 100 is abox heater such as a cabin heater including a peaked roof. According toan alternative embodiment, the enclosed heater burner system 100incorporates a vertical cylindrical heater. Those of skill in the artwill recognize, in light of the present disclosure, that a perforatedflame holder 102 can be utilized in a large variety of types of enclosedheaters in accordance with principles of the present disclosure. Alltypes of enclosed heaters fall within the scope of the presentdisclosure.

FIG. 2 is a simplified diagram of a burner system 200 including aperforated flame holder 102 configured to hold a combustion reaction,according to an embodiment. As used herein, the terms perforated flameholder, perforated reaction holder, porous flame holder, porous reactionholder, duplex, and duplex tile shall be considered synonymous unlessfurther definition is provided.

Experiments performed by the inventors have shown that perforated flameholders 102 described herein can support very clean combustion.Specifically, in experimental use of systems 200 ranging from pilotscale to full scale, output of oxides of nitrogen (NOx) was measured torange from low single digit parts per million (ppm) down to undetectable(less than 1 ppm) concentration of NOx at the stack. These remarkableresults were measured at 3% (dry) oxygen (O₂) concentration withundetectable carbon monoxide (CO) at stack temperatures typical ofindustrial furnace applications (1400-1600° F.). Moreover, these resultsdid not require any extraordinary measures such as selective catalyticreduction (SCR), selective non-catalytic reduction (SNCR), water/steaminjection, external flue gas recirculation (FGR), or other heroicextremes that may be required for conventional burners to even approachsuch clean combustion.

According to embodiments, the burner system 200 includes a fuel andoxidant source 202 disposed to output fuel and oxidant into a combustionvolume 204 to form a fuel and oxidant mixture 206. As used herein, theterms fuel and oxidant mixture and fuel stream may be usedinterchangeably and considered synonymous depending on the context,unless further definition is provided. As used herein, the termscombustion volume, combustion chamber, furnace volume, and the likeshall be considered synonymous unless further definition is provided.The perforated flame holder 102 is disposed in the combustion volume 204and positioned to receive the fuel and oxidant mixture 206.

FIG. 3 is a side sectional diagram 300 of a portion of the perforatedflame holder 102 of FIGS. 1 and 2, according to an embodiment. Referringto FIGS. 2 and 3, the perforated flame holder 102 includes a perforatedflame holder body 208 defining a plurality of perforations 210 alignedto receive the fuel and oxidant mixture 206 from the fuel and oxidantsource 202. As used herein, the terms perforation, pore, aperture,elongated aperture, and the like, in the context of the perforated flameholder 102, shall be considered synonymous unless further definition isprovided. The perforations 210 are configured to collectively hold acombustion reaction 302 supported by the fuel and oxidant mixture 206.

The fuel can include hydrogen, a hydrocarbon gas, a vaporizedhydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered orpulverized solid. The fuel can be a single species or can include amixture of gas(es), vapor(s), atomized liquid(s), and/or pulverizedsolid(s). For example, in a process heater application the fuel caninclude fuel gas or byproducts from the process that include carbonmonoxide (CO), hydrogen (H₂), and methane (CH₄). In another applicationthe fuel can include natural gas (mostly CH₄) or propane (C₃H₈). Inanother application, the fuel can include #2 fuel oil or #6 fuel oil.Dual fuel applications and flexible fuel applications are similarlycontemplated by the inventors. The oxidant can include oxygen carried byair, flue gas, and/or can include another oxidant, either pure orcarried by a carrier gas. The terms oxidant and oxidizer shall beconsidered synonymous herein.

According to an embodiment, the perforated flame holder body 208 can bebounded by an input face 212 disposed to receive the fuel and oxidantmixture 206, an output face 214 facing away from the fuel and oxidantsource 202, and a peripheral surface 216 defining a lateral extent ofthe perforated flame holder 102. The plurality of perforations 210 whichare defined by the perforated flame holder body 208 extend from theinput face 212 to the output face 214. The plurality of perforations 210can receive the fuel and oxidant mixture 206 at the input face 212. Thefuel and oxidant mixture 206 can then combust in or near the pluralityof perforations 210 and combustion products can exit the plurality ofperforations 210 at or near the output face 214.

According to an embodiment, the perforated flame holder 102 isconfigured to hold a majority of the combustion reaction 302 within theperforations 210. For example, on a steady-state basis, more than halfthe molecules of fuel output into the combustion volume 204 by the fueland oxidant source 202 may be converted to combustion products betweenthe input face 212 and the output face 214 of the perforated flameholder 102. According to an alternative interpretation, more than halfof the heat or thermal energy output by the combustion reaction 302 maybe output between the input face 212 and the output face 214 of theperforated flame holder 102. As used herein, the terms heat, heatenergy, and thermal energy shall be considered synonymous unless furtherdefinition is provided. As used above, heat energy and thermal energyrefer generally to the released chemical energy initially held byreactants during the combustion reaction 302. As used elsewhere herein,heat, heat energy and thermal energy correspond to a detectabletemperature rise undergone by real bodies characterized by heatcapacities. Under nominal operating conditions, the perforations 210 canbe configured to collectively hold at least 80% of the combustionreaction 302 between the input face 212 and the output face 214 of theperforated flame holder 102. In some experiments, the inventors produceda combustion reaction 302 that was apparently wholly contained in theperforations 210 between the input face 212 and the output face 214 ofthe perforated flame holder 102. According to an alternativeinterpretation, the perforated flame holder 102 can support combustionbetween the input face 212 and output face 214 when combustion is“time-averaged.” For example, during transients, such as before theperforated flame holder 102 is fully heated, or if too high a (cooling)load is placed on the system, the combustion may travel somewhatdownstream from the output face 214 of the perforated flame holder 102.Alternatively, if the cooling load is relatively low and/or the furnacetemperature reaches a high level, the combustion may travel somewhatupstream of the input face 212 of the perforated flame holder 102.

While a “flame” is described in a manner intended for ease ofdescription, it should be understood that in some instances, no visibleflame is present. Combustion occurs primarily within the perforations210, but the “glow” of combustion heat is dominated by a visible glow ofthe perforated flame holder 102 itself. In other instances, theinventors have noted transient “huffing” or “flashback” wherein avisible flame momentarily ignites in a region lying between the inputface 212 of the perforated flame holder 102 and the fuel nozzle 218,within the dilution region D_(D). Such transient huffing or flashback isgenerally short in duration such that, on a time-averaged basis, amajority of combustion occurs within the perforations 210 of theperforated flame holder 102, between the input face 212 and the outputface 214. In still other instances, the inventors have noted apparentcombustion occurring downstream from the output face 214 of theperforated flame holder 102, but still a majority of combustion occurredwithin the perforated flame holder 102 as evidenced by continued visibleglow from the perforated flame holder 102 that was observed.

The perforated flame holder 102 can be configured to receive heat fromthe combustion reaction 302 and output a portion of the received heat asthermal radiation 304 to heat-receiving structures (e.g., furnace wallsand/or radiant section working fluid tubes) in or adjacent to thecombustion volume 204. As used herein, terms such as radiation, thermalradiation, radiant heat, heat radiation, etc. are to be construed asbeing substantially synonymous, unless further definition is provided.Specifically, such terms refer to blackbody-type radiation ofelectromagnetic energy, primarily at infrared wavelengths, but also atvisible wavelengths owing to elevated temperature of the perforatedflame holder body 208.

Referring especially to FIG. 3, the perforated flame holder 102 outputsanother portion of the received heat to the fuel and oxidant mixture 206received at the input face 212 of the perforated flame holder 102. Theperforated flame holder body 208 may receive heat from the combustionreaction 302 at least in heat receiving regions 306 of perforation walls308. Experimental evidence has suggested to the inventors that theposition of the heat receiving regions 306, or at least the positioncorresponding to a maximum rate of receipt of heat, can vary along thelength of the perforation walls 308. In some experiments, the locationof maximum receipt of heat was apparently between ⅓ and ½ of thedistance from the input face 212 to the output face 214 (i.e., somewhatnearer to the input face 212 than to the output face 214). The inventorscontemplate that the heat receiving regions 306 may lie nearer to theoutput face 214 of the perforated flame holder 102 under otherconditions. Most probably, there is no clearly defined edge of the heatreceiving regions 306 (or for that matter, the heat output regions 310,described below). For ease of understanding, the heat receiving regions306 and the heat output regions 310 will be described as particularregions 306, 310.

The perforated flame holder body 208 can be characterized by a heatcapacity. The perforated flame holder body 208 may hold thermal energyfrom the combustion reaction 302 in an amount corresponding to the heatcapacity multiplied by temperature rise, and transfer the thermal energyfrom the heat receiving regions 306 to heat output regions 310 of theperforation walls 308. Generally, the heat output regions 310 are nearerto the input face 212 than are the heat receiving regions 306. Accordingto one interpretation, the perforated flame holder body 208 can transferheat from the heat receiving regions 306 to the heat output regions 310via thermal radiation, depicted graphically as 304. According to anotherinterpretation, the perforated flame holder body 208 can transfer heatfrom the heat receiving regions 306 to the heat output regions 310 viaheat conduction along heat conduction paths 312. The inventorscontemplate that multiple heat transfer mechanisms including conduction,radiation, and possibly convection may be operative in transferring heatfrom the heat receiving regions 306 to the heat output regions 310. Inthis way, the perforated flame holder 102 may act as a heat source tomaintain the combustion reaction 302, even under conditions where acombustion reaction 302 would not be stable when supported from aconventional flame holder.

The inventors believe that the perforated flame holder 102 causes thecombustion reaction 302 to begin within thermal boundary layers 314formed adjacent to walls 308 of the perforations 210. Insofar ascombustion is generally understood to include a large number ofindividual reactions, and since a large portion of combustion energy isreleased within the perforated flame holder 102, it is apparent that atleast a majority of the individual reactions occur within the perforatedflame holder 102. As the relatively cool fuel and oxidant mixture 206approaches the input face 212, the flow is split into portions thatrespectively travel through individual perforations 210. The hotperforated flame holder body 208 transfers heat to the fluid, notablywithin thermal boundary layers 314 that progressively thicken as moreand more heat is transferred to the incoming fuel and oxidant mixture206. After reaching a combustion temperature (e.g., the auto-ignitiontemperature of the fuel), the reactants continue to flow while achemical ignition delay time elapses, over which time the combustionreaction 302 occurs. Accordingly, the combustion reaction 302 is shownas occurring within the thermal boundary layers 314. As flow progresses,the thermal boundary layers 314 merge at a merger point 316. Ideally,the merger point 316 lies between the input face 212 and output face 214that define the ends of the perforations 210. At some position along thelength of a perforation 210, the combustion reaction 302 outputs moreheat to the perforated flame holder body 208 than it receives from theperforated flame holder body 208. The heat is received at the heatreceiving region 306, is held by the perforated flame holder body 208,and is transported to the heat output region 310 nearer to the inputface 212, where the heat is transferred into the cool reactants (and anyincluded diluent) to bring the reactants to the ignition temperature.

In an embodiment, each of the perforations 210 is characterized by alength L defined as a reaction fluid propagation path length between theinput face 212 and the output face 214 of the perforated flame holder102. As used herein, the term reaction fluid refers to matter thattravels through a perforation 210. Near the input face 212, the reactionfluid includes the fuel and oxidant mixture 206 (optionally includingnitrogen, flue gas, and/or other “non-reactive” species). Within thecombustion reaction region, the reaction fluid may include plasmaassociated with the combustion reaction 302, molecules of reactants andtheir constituent parts, any non-reactive species, reactionintermediates (including transition states), and reaction products. Nearthe output face 214, the reaction fluid may include reaction productsand byproducts, non-reactive gas, and excess oxidant.

The plurality of perforations 210 can be each characterized by atransverse dimension D between opposing perforation walls 308. Theinventors have found that stable combustion can be maintained in theperforated flame holder 102 if the length L of each perforation 210 isat least four times the transverse dimension D of the perforation. Inother embodiments, the length L can be greater than six times thetransverse dimension D. For example, experiments have been run where Lis at least eight, at least twelve, at least sixteen, and at leasttwenty-four times the transverse dimension D. Preferably, the length Lis sufficiently long for thermal boundary layers 314 to form adjacent tothe perforation walls 308 in a reaction fluid flowing through theperforations 210 to converge at merger points 316 within theperforations 210 between the input face 212 and the output face 214 ofthe perforated flame holder 102. In experiments, the inventors havefound L/D ratios between 12 and 48 to work well (i.e., produce low NOx,produce low CO, and maintain stable combustion).

The perforated flame holder body 208 can be configured to convey heatbetween adjacent perforations 210. The heat conveyed between adjacentperforations 210 can be selected to cause heat output from thecombustion reaction portion 302 in a first perforation 210 to supplyheat to stabilize a combustion reaction portion 302 in an adjacentperforation 210.

Referring especially to FIG. 2, the fuel and oxidant source 202 canfurther include a fuel nozzle 218, configured to output fuel, and anoxidant source 220 configured to output a fluid including the oxidant.For example, the fuel nozzle 218 can be configured to output pure fuel.The oxidant source 220 can be configured to output combustion aircarrying oxygen, and optionally, flue gas.

The perforated flame holder 102 can be held by a perforated flame holdersupport structure 222 configured to hold the perforated flame holder 102at a dilution distance D_(D) away from the fuel nozzle 218. The fuelnozzle 218 can be configured to emit a fuel jet selected to entrain theoxidant to form the fuel and oxidant mixture 206 as the fuel jet andoxidant travel along a path to the perforated flame holder 102 throughthe dilution distance D_(D) between the fuel nozzle 218 and theperforated flame holder 102. Additionally or alternatively (particularlywhen a blower is used to deliver oxidant contained in combustion air),the oxidant or combustion air source can be configured to entrain thefuel and the fuel and oxidant travel through the dilution distanceD_(D). In some embodiments, a flue gas recirculation path 224 can beprovided. Additionally or alternatively, the fuel nozzle 218 can beconfigured to emit a fuel jet selected to entrain the oxidant and toentrain flue gas as the fuel jet travels through the dilution distanceD_(D) between the fuel nozzle 218 and the input face 212 of theperforated flame holder 102.

The fuel nozzle 218 can be configured to emit the fuel through one ormore fuel orifices 226 having an inside diameter dimension that isreferred to as “nozzle diameter.” The perforated flame holder supportstructure 222 can support the perforated flame holder 102 to receive thefuel and oxidant mixture 206 at the distance D_(D) away from the fuelnozzle 218 greater than 20 times the nozzle diameter. In anotherembodiment, the perforated flame holder 102 is disposed to receive thefuel and oxidant mixture 206 at the distance D_(D) away from the fuelnozzle 218 between 100 times and 1100 times the nozzle diameter.Preferably, the perforated flame holder support structure 222 isconfigured to hold the perforated flame holder 102 at a distance about200 times or more of the nozzle diameter away from the fuel nozzle 218.When the fuel and oxidant mixture 206 travels about 200 times the nozzlediameter or more, the mixture is sufficiently homogenized to cause thecombustion reaction 302 to produce minimal NOx.

The fuel and oxidant source 202 can alternatively include a premix fueland oxidant source, according to an embodiment. A premix fuel andoxidant source can include a premix chamber (not shown), a fuel nozzleconfigured to output fuel into the premix chamber, and an oxidant (e.g.,combustion air) channel configured to output the oxidant into the premixchamber. A flame arrestor can be disposed between the premix fuel andoxidant source and the perforated flame holder 102 and be configured toprevent flame flashback into the premix fuel and oxidant source.

The oxidant source 220, whether configured for entrainment in thecombustion volume 204 or for premixing, can include a blower configuredto force the oxidant through the fuel and oxidant source 202.

The support structure 222 can be configured to support the perforatedflame holder 102 from a floor or wall (not shown) of the combustionvolume 204, for example. In another embodiment, the support structure222 supports the perforated flame holder 102 from the fuel and oxidantsource 202. Alternatively, the support structure 222 can suspend theperforated flame holder 102 from an overhead structure (such as a flue,in the case of an up-fired system). The support structure 222 cansupport the perforated flame holder 102 in various orientations anddirections.

The perforated flame holder 102 can include a single perforated flameholder body 208. In another embodiment, the perforated flame holder 102can include a plurality of adjacent perforated flame holder sectionsthat collectively provide a tiled perforated flame holder 102.

The perforated flame holder support structure 222 can be configured tosupport the plurality of perforated flame holder sections. Theperforated flame holder support structure 222 can include a metalsuperalloy, a cementatious, and/or ceramic refractory material. In anembodiment, the plurality of adjacent perforated flame holder sectionscan be joined with a fiber reinforced refractory cement.

The perforated flame holder 102 can have a width dimension W betweenopposite sides of the peripheral surface 216 at least twice a thicknessdimension T between the input face 212 and the output face 214. Inanother embodiment, the perforated flame holder 102 can have a widthdimension W between opposite sides of the peripheral surface 216 atleast three times, at least six times, or at least nine times thethickness dimension T between the input face 212 and the output face 214of the perforated flame holder 102.

In an embodiment, the perforated flame holder 102 can have a widthdimension W less than a width of the combustion volume 204. This canallow the flue gas circulation path 224 from above to below theperforated flame holder 102 to lie between the peripheral surface 216 ofthe perforated flame holder 102 and the combustion volume wall (notshown).

Referring again to both FIGS. 2 and 3, the perforations 210 can be ofvarious shapes. In an embodiment, the perforations 210 can includeelongated squares, each having a transverse dimension D between opposingsides of the squares. In another embodiment, the perforations 210 caninclude elongated hexagons, each having a transverse dimension D betweenopposing sides of the hexagons. In yet another embodiment, theperforations 210 can include hollow cylinders, each having a transversedimension D corresponding to a diameter of the cylinder. In anotherembodiment, the perforations 210 can include truncated cones ortruncated pyramids (e.g., frustums), each having a transverse dimensionD radially symmetric relative to a length axis that extends from theinput face 212 to the output face 214. In some embodiments, theperforations 210 can each have a lateral dimension D equal to or greaterthan a quenching distance of the flame based on standard referenceconditions. Alternatively, the perforations 210 may have lateraldimension D less then than a standard reference quenching distance.

In one range of embodiments, each of the plurality of perforations 210has a lateral dimension D between 0.05 inch and 1.0 inch. Preferably,each of the plurality of perforations 210 has a lateral dimension Dbetween 0.1 inch and 0.5 inch. For example the plurality of perforations210 can each have a lateral dimension D of about 0.2 to 0.4 inch.

The void fraction of a perforated flame holder 102 is defined as thetotal volume of all perforations 210 in a section of the perforatedflame holder 102 divided by a total volume of the perforated flameholder 102 including body 208 and perforations 210. The perforated flameholder 102 should have a void fraction between 0.10 and 0.90. In anembodiment, the perforated flame holder 102 can have a void fractionbetween 0.30 and 0.80. In another embodiment, the perforated flameholder 102 can have a void fraction of about 0.70. Using a void fractionof about 0.70 was found to be especially effective for producing verylow NOx.

The perforated flame holder 102 can be formed from a fiber reinforcedcast refractory material and/or a refractory material such as analuminum silicate material. For example, the perforated flame holder 102can be formed to include mullite or cordierite. Additionally oralternatively, the perforated flame holder body 208 can include a metalsuperalloy such as Inconel or Hastelloy. The perforated flame holderbody 208 can define a honeycomb. Honeycomb is an industrial term of artthat need not strictly refer to a hexagonal cross section and mostusually includes cells of square cross section. Honeycombs of othercross sectional areas are also known.

The inventors have found that the perforated flame holder 102 can beformed from VERSAGRID® ceramic honeycomb, available from AppliedCeramics, Inc. of Doraville, S.C.

The perforations 210 can be parallel to one another and normal to theinput and output faces 212, 214. In another embodiment, the perforations210 can be parallel to one another and formed at an angle relative tothe input and output faces 212, 214. In another embodiment, theperforations 210 can be non-parallel to one another. In anotherembodiment, the perforations 210 can be non-parallel to one another andnon-intersecting. In another embodiment, the perforations 210 can beintersecting. The body 308 can be one piece or can be formed from aplurality of sections.

In another embodiment, which is not necessarily preferred, theperforated flame holder 102 may be formed from reticulated ceramicmaterial. The term “reticulated” refers to a netlike structure.Reticulated ceramic material is often made by dissolving a slurry into asponge of specified porosity, allowing the slurry to harden, and burningaway the sponge and curing the ceramic.

In another embodiment, which is not necessarily preferred, theperforated flame holder 102 may be formed from a ceramic material thathas been punched, bored or cast to create channels.

In another embodiment, the perforated flame holder 102 can include aplurality of tubes or pipes bundled together. The plurality ofperforations 210 can include hollow cylinders and can optionally alsoinclude interstitial spaces between the bundled tubes. In an embodiment,the plurality of tubes can include ceramic tubes. Refractory cement canbe included between the tubes and configured to adhere the tubestogether. In another embodiment, the plurality of tubes can includemetal (e.g., superalloy) tubes. The plurality of tubes can be heldtogether by a metal tension member circumferential to the plurality oftubes and arranged to hold the plurality of tubes together. The metaltension member can include stainless steel, a superalloy metal wire,and/or a superalloy metal band.

The perforated flame holder body 208 can alternatively include stackedperforated sheets of material, each sheet having openings that connectwith openings of subjacent and superjacent sheets. The perforated sheetscan include perforated metal sheets, ceramic sheets and/or expandedsheets. In another embodiment, the perforated flame holder body 208 caninclude discontinuous packing bodies such that the perforations 210 areformed in the interstitial spaces between the discontinuous packingbodies. In one example, the discontinuous packing bodies includestructured packing shapes. In another example, the discontinuous packingbodies include random packing shapes. For example, the discontinuouspacking bodies can include ceramic Raschig ring, ceramic Berl saddles,ceramic Intalox saddles, and/or metal rings or other shapes (e.g. SuperRaschig Rings) that may be held together by a metal cage.

The inventors contemplate various explanations for why burner systemsincluding the perforated flame holder 102 provide such clean combustion.

According to an embodiment, the perforated flame holder 102 may act as aheat source to maintain a combustion reaction even under conditionswhere a combustion reaction would not be stable when supported by aconventional flame holder. This capability can be leveraged to supportcombustion using a leaner fuel-to-oxidant mixture than is typicallyfeasible. Thus, according to an embodiment, at the point where the fuelstream 206 contacts the input face 212 of the perforated flame holder102, an average fuel-to-oxidant ratio of the fuel stream 206 is below a(conventional) lower combustion limit of the fuel component of the fuelstream 206—lower combustion limit defines the lowest concentration offuel at which a fuel and oxidant mixture 206 will burn when exposed to amomentary ignition source under normal atmospheric pressure and anambient temperature of 25° C. (77° F.).

The perforated flame holder 102 and systems including the perforatedflame holder 102 described herein were found to provide substantiallycomplete combustion of CO (single digit ppm down to undetectable,depending on experimental conditions), while supporting low NOx.According to one interpretation, such a performance can be achieved dueto a sufficient mixing used to lower peak flame temperatures (amongother strategies). Flame temperatures tend to peak under slightly richconditions, which can be evident in any diffusion flame that isinsufficiently mixed. By sufficiently mixing, a homogenous and slightlylean mixture can be achieved prior to combustion. This combination canresult in reduced flame temperatures, and thus reduced NOx formation. Inone embodiment, “slightly lean” may refer to 3% O₂, i.e. an equivalenceratio of ˜0.87. Use of even leaner mixtures is possible, but may resultin elevated levels of O₂. Moreover, the inventors believe perforationwalls 308 may act as a heat sink for the combustion fluid. This effectmay alternatively or additionally reduce combustion temperatures andlower NOx.

According to another interpretation, production of NOx can be reduced ifthe combustion reaction 302 occurs over a very short duration of time.Rapid combustion causes the reactants (including oxygen and entrainednitrogen) to be exposed to NOx-formation temperature for a time tooshort for NOx formation kinetics to cause significant production of NOx.The time required for the reactants to pass through the perforated flameholder 102 is very short compared to a conventional flame. The low NOxproduction associated with perforated flame holder combustion may thusbe related to the short duration of time required for the reactants (andentrained nitrogen) to pass through the perforated flame holder 102.

FIG. 4 is a flow chart showing a method 400 for operating a burnersystem including the perforated flame holder shown and described herein.To operate a burner system including a perforated flame holder, theperforated flame holder is first heated to a temperature sufficient tomaintain combustion of the fuel and oxidant mixture.

According to a simplified description, the method 400 begins with step402, wherein the perforated flame holder is preheated to a start-uptemperature, T_(S). After the perforated flame holder is raised to thestart-up temperature, the method proceeds to step 404, wherein the fueland oxidant are provided to the perforated flame holder and combustionis held by the perforated flame holder.

According to a more detailed description, step 402 begins with step 406,wherein start-up energy is provided at the perforated flame holder.Simultaneously or following providing start-up energy, a decision step408 determines whether the temperature T of the perforated flame holderis at or above the start-up temperature, T_(S). As long as thetemperature of the perforated flame holder is below its start-uptemperature, the method loops between steps 406 and 408 within thepreheat step 402. In step 408, if the temperature T of at least apredetermined portion of the perforated flame holder is greater than orequal to the start-up temperature, the method 400 proceeds to overallstep 404, wherein fuel and oxidant is supplied to and combustion is heldby the perforated flame holder.

Step 404 may be broken down into several discrete steps, at least someof which may occur simultaneously.

Proceeding from step 408, a fuel and oxidant mixture is provided to theperforated flame holder, as shown in step 410. The fuel and oxidant maybe provided by a fuel and oxidant source that includes a separate fuelnozzle and oxidant (e.g., combustion air) source, for example. In thisapproach, the fuel and oxidant are output in one or more directionsselected to cause the fuel and oxidant mixture to be received by theinput face of the perforated flame holder. The fuel may entrain thecombustion air (or alternatively, the combustion air may dilute thefuel) to provide a fuel and oxidant mixture at the input face of theperforated flame holder at a fuel dilution selected for a stablecombustion reaction that can be held within the perforations of theperforated flame holder.

Proceeding to step 412, the combustion reaction is held by theperforated flame holder.

In step 414, heat may be output from the perforated flame holder. Theheat output from the perforated flame holder may be used to power anindustrial process, heat a working fluid, generate electricity, orprovide motive power, for example.

In optional step 416, the presence of combustion may be sensed. Varioussensing approaches have been used and are contemplated by the inventors.Generally, combustion held by the perforated flame holder is very stableand no unusual sensing requirement is placed on the system. Combustionsensing may be performed using an infrared sensor, a video sensor, anultraviolet sensor, a charged species sensor, thermocouple, thermopile,flame rod, and/or other combustion sensing apparatuses. In an additionalor alternative variant of step 416, a pilot flame or other ignitionsource may be provided to cause ignition of the fuel and oxidant mixturein the event combustion is lost at the perforated flame holder.

Proceeding to decision step 418, if combustion is sensed not to bestable, the method 400 may exit to step 424, wherein an error procedureis executed. For example, the error procedure may include turning offfuel flow, re-executing the preheating step 402, outputting an alarmsignal, igniting a stand-by combustion system, or other steps. If, instep 418, combustion in the perforated flame holder is determined to bestable, the method 400 proceeds to decision step 420, wherein it isdetermined if combustion parameters should be changed. If no combustionparameters are to be changed, the method loops (within step 404) back tostep 410, and the combustion process continues. If a change incombustion parameters is indicated, the method 400 proceeds to step 422,wherein the combustion parameter change is executed. After changing thecombustion parameter(s), the method loops (within step 404) back to step410, and combustion continues.

Combustion parameters may be scheduled to be changed, for example, if achange in heat demand is encountered. For example, if less heat isrequired (e.g., due to decreased electricity demand, decreased motivepower requirement, or lower industrial process throughput), the fuel andoxidant flow rate may be decreased in step 422. Conversely, if heatdemand is increased, then fuel and oxidant flow may be increased.Additionally or alternatively, if the combustion system is in a start-upmode, then fuel and oxidant flow may be gradually increased to theperforated flame holder over one or more iterations of the loop withinstep 404.

Referring again to FIG. 2, the burner system 200 includes a heater 228operatively coupled to the perforated flame holder 102. As described inconjunction with FIGS. 3 and 4, the perforated flame holder 102 operatesby outputting heat to the incoming fuel and oxidant mixture 206. Aftercombustion is established, this heat is provided by the combustionreaction 302; but before combustion is established, the heat is providedby the heater 228.

Various heating apparatuses have been used and are contemplated by theinventors. In some embodiments, the heater 228 can include a flameholder configured to support a flame disposed to heat the perforatedflame holder 102. The fuel and oxidant source 202 can include a fuelnozzle 218 configured to emit a fuel stream 206 and an oxidant source220 configured to output oxidant (e.g., combustion air) adjacent to thefuel stream 206. The fuel nozzle 218 and oxidant source 220 can beconfigured to output the fuel stream 206 to be progressively diluted bythe oxidant (e.g., combustion air). The perforated flame holder 102 canbe disposed to receive a diluted fuel and oxidant mixture 206 thatsupports a combustion reaction 302 that is stabilized by the perforatedflame holder 102 when the perforated flame holder 102 is at an operatingtemperature. A start-up flame holder, in contrast, can be configured tosupport a start-up flame at a location corresponding to a relativelyunmixed fuel and oxidant mixture that is stable without stabilizationprovided by the heated perforated flame holder 102.

The burner system 200 can further include a controller 230 operativelycoupled to the heater 228 and to a data interface 232. For example, thecontroller 230 can be configured to control a start-up flame holderactuator configured to cause the start-up flame holder to hold thestart-up flame when the perforated flame holder 102 needs to bepre-heated and to not hold the start-up flame when the perforated flameholder 102 is at an operating temperature (e.g., when T≧T_(S)).

Various approaches for actuating a start-up flame are contemplated. Inone embodiment, the start-up flame holder includes amechanically-actuated bluff body configured to be actuated to interceptthe fuel and oxidant mixture 206 to cause heat-recycling and/orstabilizing vortices and thereby hold a start-up flame; or to beactuated to not intercept the fuel and oxidant mixture 206 to cause thefuel and oxidant mixture 206 to proceed to the perforated flame holder102. In another embodiment, a fuel control valve, blower, and/or dampermay be used to select a fuel and oxidant mixture flow rate that issufficiently low for a start-up flame to be jet-stabilized; and uponreaching a perforated flame holder 102 operating temperature, the flowrate may be increased to “blow out” the start-up flame. In anotherembodiment, the heater 228 may include an electrical power supplyoperatively coupled to the controller 230 and configured to apply anelectrical charge or voltage to the fuel and oxidant mixture 206. Anelectrically conductive start-up flame holder may be selectively coupledto a voltage ground or other voltage selected to attract the electricalcharge in the fuel and oxidant mixture 206. The attraction of theelectrical charge was found by the inventors to cause a start-up flameto be held by the electrically conductive start-up flame holder.

In another embodiment, the heater 228 may include an electricalresistance heater configured to output heat to the perforated flameholder 102 and/or to the fuel and oxidant mixture 206. The electricalresistance heater can be configured to heat up the perforated flameholder 102 to an operating temperature. The heater 228 can furtherinclude a power supply and a switch operable, under control of thecontroller 230, to selectively couple the power supply to the electricalresistance heater.

An electrical resistance heater 228 can be formed in various ways. Forexample, the electrical resistance heater 228 can be formed fromKANTHAL® wire (available from Sandvik Materials Technology division ofSandvik AB of Hallstahammar, Sweden) threaded through at least a portionof the perforations 210 defined by the perforated flame holder body 208.Alternatively, the heater 228 can include an inductive heater, ahigh-energy beam heater (e.g. microwave or laser), a frictional heater,electro-resistive ceramic coatings, or other types of heatingtechnologies.

Other forms of start-up apparatuses are contemplated. For example, theheater 228 can include an electrical discharge igniter or hot surfaceigniter configured to output a pulsed ignition to the oxidant and fuel.Additionally or alternatively, a start-up apparatus can include a pilotflame apparatus disposed to ignite the fuel and oxidant mixture 206 thatwould otherwise enter the perforated flame holder 102. The electricaldischarge igniter, hot surface igniter, and/or pilot flame apparatus canbe operatively coupled to the controller 230, which can cause theelectrical discharge igniter or pilot flame apparatus to maintaincombustion of the fuel and oxidant mixture 206 in or upstream from theperforated flame holder 102 before the perforated flame holder 102 isheated sufficiently to maintain combustion.

The burner system 200 can further include a sensor 234 operativelycoupled to the control circuit 230. The sensor 234 can include a heatsensor configured to detect infrared radiation or a temperature of theperforated flame holder 102. The control circuit 230 can be configuredto control the heating apparatus 228 responsive to input from the sensor234. Optionally, a fuel control valve 236 can be operatively coupled tothe controller 230 and configured to control a flow of fuel to the fueland oxidant source 202. Additionally or alternatively, an oxidant bloweror damper 238 can be operatively coupled to the controller 230 andconfigured to control flow of the oxidant (or combustion air).

The sensor 234 can further include a combustion sensor operativelycoupled to the control circuit 230, the combustion sensor beingconfigured to detect a temperature, video image, and/or spectralcharacteristic of a combustion reaction held by the perforated flameholder 102. The fuel control valve 236 can be configured to control aflow of fuel from a fuel source to the fuel and oxidant source 202. Thecontroller 230 can be configured to control the fuel control valve 236responsive to input from the combustion sensor 234. The controller 230can be configured to control the fuel control valve 236 and/or oxidantblower or damper to control a preheat flame type of heater 228 to heatthe perforated flame holder 102 to an operating temperature. Thecontroller 230 can similarly control the fuel control valve 236 and/orthe oxidant blower or damper to change the fuel and oxidant mixture 206flow responsive to a heat demand change received as data via the datainterface 232.

FIG. 5A is a perspective view of a cabin heater 500, according to anembodiment. The cabin heater 500 includes sidewalls 510 a-510 d, thoughonly sidewalls 510 a, 510 b are visible in FIG. 5A. The cabin heater 500further includes sloped roof portions 514 a-d (only 514 a and 514 b arevisible), and a flat roof peak portion 516. A flue vent 518 ispositioned on roof peak 516. The flue vent 518 vents flue gases from aninterior of the cabin heater 500 to an exterior of the cabin heater 500.A first tube 506 a passes through the sidewall 510 into the interior ofthe cabin heater 500. A second tube 506 b also passes from the exteriorof the cabin heater 500 to the interior of the cabin heater 500. Aworking fluid 108 passes into the tube 506 a via an input 520 a. Aworking fluid 108 passes into the tube 506 b via a second input 520 b.

FIG. 5B is a top view of the cabin heater 500, according to oneembodiment. All four of the sloped roof portions 514 a-514 d and theroof peak 516 are visible in the top view of FIG. 5B. Additionally,output portions 522 a, 522 b of the tubes 506 a, 506 b are visible. Inparticular, the working fluid 108 is passed from the tube 506 a via anoutput 522 a. The working fluid 108 is passed from the tube 506 b viathe output 522 b.

FIG. 5C is a cross-section of the cabin heater 500 taken alongcross-section lines 5C from FIG. 5B, according to an embodiment. FIG. 5Cillustrates that the tube 506 a lines the sidewall 510 d and the slopedroof portion 514 d within the interior volume 512 of the cabin heater500. Multiple portions of the tube 506 a are visible in FIG. 5C becausethe tube 506 a runs in a serpentine manner along the sidewall 510 d andthe sloped roof portion 514 d, as is further apparent with reference toFIG. 5D. The tube 506 b lines the sidewall 510 b and the sloped roofportion 514 b. Multiple portions of the tube 506 b are visible in FIG.5C because the tube 506 b runs in a serpentine manner along the sidewall510 b and the sloped roof portion 514 b as is further apparent withreference to FIG. 5D. A perforated flame holder 102 is positioned in theinterior volume 512 between the tubes 506 a and 506 b and above a fueland oxidant source 524.

The fuel and oxidant source 524 outputs fuel and oxidant 526 onto theperforated flame holder 102. The perforated flame holder 102 supports acombustion reaction of the fuel and oxidant 526 within the perforatedflame holder 102. The perforated flame holder 102 absorbs heat from thecombustion reaction of the fuel and oxidant 526. The perforated flameholder 102 radiates heat to the tubes 506 a, 506 b. As the working fluid508 passes through the multiple serpentine portions of the tubes 506 a,506 b, heat from the perforated flame holder 102 is transferred to theworking fluid 508 in the tubes 506 a, 506 b. When the working fluid 508passes from the outputs 522 a, 522 b the working fluid has absorbed alarge amount of heat. In this way, the working fluid 508 transfers heatfrom the combustion reaction of the fuel and oxidant 526 to the exteriorof the cabin heater 500.

According to an embodiment, the working fluid 508 is crude oil.Alternatively, the working fluid 508 can include natural gas, otherhydrocarbon products, water, glycol water, air, or regeneration gas.Those skilled in the art will recognize, in light of the presentdisclosure, that the working fluid 508 can include many other fluids.

According to an embodiment, the fuel and oxidant source 524 protrudesthrough the floor of the cabin heater 500. Only the portion of the fueland oxidant source 524 that is positioned within the cabin heater 500 isshown in FIG. 5C and FIG. 5D.

FIG. 5D is a side view of the interior volume 512 of the cabin heater500 viewed from the cross-section lines 5D of FIG. 5B. The perforatedflame holder 102 and the fuel and oxidant source 524 are visible in theforeground. The tube 506 a is visible in the background. In particular,the serpentine layout of the tube 506 a is more readily apparent in theside view of FIG. 5D.

Although a cabin heater 500 has been shown with respect to FIGS. 5A-5D,those of skill in the art will recognize, in light of the presentdisclosure, that many other types of box heaters can implement aperforated flame holder 102. For example, a box heater can have acylindrical outer wall with one or more tubes lining the inside of thewall and a perforated flame holder 102 positioned in an interior volumeof the box heater.

According to an embodiment, multiple tubes 506 can be positioned on eachwall of the cabin heater 500. The multiple tubes 506 can be wound abouteach other. Those skilled in the art will recognize, in light of thepresent disclosure, that many other configurations for tubes 506 withinthe cabin heater 500 are possible. All such other configurations fallwithin the scope of the present disclosure.

FIG. 6 is a side view of an interior volume 612 of a box heater 600,according to an embodiment. Multiple perforated flame holders 102 a-102c are positioned in the interior volume 612 of the box heater 600. Atube 606 carrying a working fluid 608 is positioned in a serpentinemanner along the wall of the box heater 600. Each perforated flameholder 102 a-102 c is positioned above a respective fuel and oxidantsource 624 a-624 c. The perforated flame holders 102 a-102 c support acombustion reaction of the fuel and oxidant output from the fuel andoxidant sources 624 a-624 c. The perforated flame holders 102 a-102 cabsorb heat from the combustion reactions and radiate heat to the tube606. A working fluid 608 within the tube 606 receives heat from the tube606. Thus, as the working fluid 608 progresses through the tube 606 itis heated by the heat radiated from the perforated flame holders 102a-102 c. The working fluid 608 is then passed from the interior volume612 of the box heater 600 to an exterior of the box heater 600.

According to an embodiment, the box heater 600 includes one or morepartitions (not shown) positioned within the interior volume 612 betweenthe first and second perforated flame holders 102 a, 102 b, and/orbetween the second and third perforated flame holders 102 b, 102 c.According to an embodiment, the one or more partitions can separate thefirst perforated flame holder 102 a from the second perforated flameholder 102 b along a line of sight between the first and secondperforated flame holders 102 a, 102 b. According to an embodiment, thepartition is configured to receive heat from the first and secondperforated flame holders 102 a, 102 b, reach an elevated temperature,and radiate heat energy to the tube 606. The partition can be a partialpartition that does not define two completely separated portions of theinterior volume 612. Alternatively, the partition can be a fullpartition that defines two completely separated portions of the interiorvolume 612.

FIG. 7 is a side view of an interior volume 712 of a box heater 700,according to one embodiment. Perforated flame holders 102 a, 102 b arepositioned laterally from respective fuel and oxidant sources 724 a, 724b. The fuel and oxidant sources 724 a, 724 b output fuel and oxidantonto the perforated flame holders 102 a, 102 b. The perforated flameholders 102 a, 102 b support a combustion reaction of the fuel andoxidant within the perforated flame holders 102 a, 102 b. A tube 706 ispositioned along a wall of the box heater 700 in a serpentine fashion. Aworking fluid 708 passes through the tube 706. The perforated flameholders 102 a, 102 b radiate heat to the tube 706, thereby heating theworking fluid 708 within the tube 706. The working fluid 708 thereforeabsorbs heat as it passes through the tube 706 within the interior 712of the heater 700.

According to an embodiment, the box heater 700 includes a partition (notshown) positioned within the interior volume between the first andsecond perforated flame holders 102 a, 102 b. According to anembodiment, the partition separates the first perforated flame holder102 a from the second perforated flame holder 102 b along a line ofsight between the first and second perforated flame holders 102 a, 102b. According to an embodiment, the partition is configured to receiveheat from the first and second flame holders 102 a, 102 b, reach anelevated temperature, and radiate heat energy to the tube 706. Thepartition can be a partial partition that does not define two completelyseparated portions of the interior volume 712. Alternatively, thepartition can be a full partition that defines two completely separatedportions of the interior volume 712.

FIG. 8 is a flow diagram of a process 800 for operating a box heater,according to an embodiment. At 802 fuel and oxidant are output from afuel and oxidant source onto a perforated flame holder. At 804, theperforated flame holder supports a combustion reaction of the fuel andoxidant within the perforated flame holder. At 806, working fluid ispassed through one or more tubes within an interior of the box heater.At 808 heat is transferred from the perforated flame holder to theworking fluid within the one or more tubes.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

1. An enclosed heater, comprising: one or more walls defining aninterior volume; a plurality of tubes positioned within the interiorvolume along one or more of the walls and configured to carry a workingfluid; a first fuel and oxidant source configured to output fuel andoxidant; and a first perforated flame holder positioned to receive thefuel and oxidant, the first perforated flame holder being configured tosupport a majority of a combustion reaction of the fuel and oxidantwithin the first perforated flame holder and to transfer heat to thetubes.
 2. The enclosed heater of claim 1, wherein the first perforatedflame holder includes: an input face proximal to the first fuel andoxidant source; an output face opposite the flame holder; and aplurality of perforations extending from the input face to the outputface and configured to receive the mixture of fuel and oxidant and tosupport the majority of the combustion reaction within the perforations.3. The enclosed heater of claim 2, wherein the first perforated flameholder is positioned laterally from the first fuel and oxidant source.4. The enclosed heater of claim 2, wherein the first perforated flameholder is positioned vertically from the first fuel and oxidant source.5. The enclosed heater of claim 1, comprising: a second fuel and oxidantsource configured to output fuel and oxidant; and a second perforatedflame holder positioned to receive the fuel and oxidant from the secondfuel and oxidant source, the second perforated flame holder configuredto support a majority of a combustion reaction of the fuel and oxidantfrom the second fuel and oxidant source within the second perforatedflame holder and to transfer heat to the tubes.
 6. The enclosed heaterof claim 5, wherein: the first perforated flame holder is positionedlaterally from the first fuel and oxidant source; the second perforatedflame holder is positioned laterally from the second fuel and oxidantsource; and the first and second perforated flame holders are positionedto transfer heat to each other.
 7. The enclosed heater of claim 5,further comprising: a partial partition separating the first perforatedflame holder from the second perforated flame holder along a line ofsight between the first and second perforated flame holders; wherein thepartial partition is configured to receive heat from the first andsecond flame holders, reach an elevated temperature, and radiate heatenergy to the tubes.
 8. The enclosed heater of claim 5, wherein: thefirst perforated flame holder is positioned above the first fuel andoxidant source; and the second perforated flame holder is positionedabove the second fuel and oxidant source.
 9. The enclosed heater ofclaim 1, wherein the working fluid is crude oil.
 10. The enclosed heaterof claim 1, wherein the enclosed heater is a crude oil pipeline heater.11. The enclosed heater of claim 1, wherein the plurality of tubes arejoined together as a single tube.
 12. The enclosed heater of claim 11,wherein the single tube is positioned along the one or more walls in aserpentine fashion.
 13. The enclosed heater of claim 1, including fourwalls and a roof.
 14. The enclosed heater of claim 13, including apeaked roof.
 15. The enclosed heater of claim 13, wherein a portion ofone or more of the plurality of tubes is positioned along a ceiling ofthe enclosed heater.
 16. The enclosed heater of claim 13, including aflue vent in the roof configured to pass flue gas from the combustionreaction from the interior volume to an exterior of the enclosed heater.17. The enclosed heater of claim 13, wherein the first fuel and oxidantsource includes one or more fuel nozzles configured to output the fueland oxidant onto the first perforated flame holder.
 18. The enclosedheater of claim 13, wherein the first fuel and oxidant source includes apremix chamber in which the fuel and oxidant are mixed prior to beingoutput to the first perforated flame holder.
 19. The enclosed heater ofclaim 1 wherein the enclosed heater is a cabin heater.
 20. The enclosedheater of claim 1 wherein the enclosed heater is a cylindrical enclosedheater.
 21. A method comprising: outputting fuel and oxidant onto afirst perforated flame holder positioned within an interior of anenclosed heater, the enclosed heater including one or more wallsdefining the interior; supporting a majority of a combustion reaction ofthe fuel and oxidant within the first perforated flame holder; passingone or more working fluids through a plurality of tubes lining the oneor more walls within the interior; and transferring heat from the firstperforated flame holder to the working fluid.
 22. The method of claim21, wherein the perforated flame holder includes an input face, anoutput face, and a plurality of perforations extending between the inputand output faces.
 23. The method of claim 22, wherein the perforatedflame holder supports a majority of a combustion reaction of the fueland oxidant within the perforations.
 24. The method of claim 21,comprising: outputting fuel and oxidant onto a second perforated flameholder positioned within the interior of the enclosed heater; supportinga second combustion reaction within the second perforated flame holder;and transferring heat from the second perforated flame holder to theworking fluid.
 25. The method of claim 21 wherein the working fluidincludes a fossil fuel.
 26. The method of claim 21 wherein the workingfluid includes water.
 27. The method of claim 21 wherein the enclosedheater is a box heater.
 28. The method of claim 21 wherein the enclosedheater is a cylindrical enclosed heater.
 29. The method of claim 21wherein the enclosed heater is a cabin heater.
 30. A box heater,comprising: an enclosure; a tube including: a first segment positionedexternal to the enclosure; a second segment positioned within theenclosure; and a third segment positioned external to the enclosure, thesecond segment connecting the first segment to the third segment, thetube being configured to pass a working fluid from the first segment,through the second segment, to the third segment; a fuel and oxidantsource positioned within the enclosure and configured to output fuel andoxidant; and a perforated flame holder positioned to receive the fueland oxidant, to sustain a combustion reaction of the fuel and oxidantwithin the perforated flame holder, and to transfer heat from thecombustion reaction to the working fluid as the working fluid passesthrough the second segment positioned within the enclosure.
 31. The boxheater of claim 30 wherein the enclosure includes one or more walls, thesecond segment being positioned adjacent to one or more of the one ormore walls.
 32. The box heater of claim 30, wherein the second segmentwinds in a serpentine fashion within the enclosure.
 33. The box heaterof claim 30 wherein the enclosure includes a vent configured to passflue gas from within the enclosure to an exterior of the enclosure.